Ya the Curve 5 is great as well according to reviews. I forget why I chose the OCTO, probably the 7-8" operating depth matched my sump perfectly, while the curve 5 is supposed to need a little deeper sump,(9"-10"?) although I'm sure it can be tuned a bit as I have read of users using the Curve 5 at 8" depth.
Also I think the OCTO has a slightly smaller, or should I say different footprint. In my case every 1/4" made a difference as my skimmer compartment is only 7 3/8" x 8 3/4".
Curve 5 - ~7 1/4" x 7"
Octo110ss - ~6" x 7 7/8"
Anyhow I'm very pleased with this skimmer, it is for all intents and purposes silent. I like that it is an AC motor, I feel I just don't need to give up the reliability of an AC pump for the adjust-ability of a DC pump in a skimmer application. (Although the new DC offerings from Coralbox piqued my interest, I went the more pragmatic route with the AC pump)
Either way, I probably would have liked the Curve 5 too if it fit.